They offered the first opportunity to explore the underwater world: bathyspheres: manned, spherical deep-sea submersibles with hatches and measuring devices. William Beebe (1877-1962) published descriptions and data of the first dives south of Bermuda. He and his colleague Otis Barton (1899-1992) collected their observations during their diving trips: they described previously unknown fishes and recorded spectroscopic measurements of the light. Internal and external temperatures were documented, as were the pressures at different depths up to 600 metres.

About a dozen of years later, researchers developed a new deep sea vessel: the 'FNRS-2', a deep diving submarine. FNRS-1 was a stratospheric balloon developed by Auguste Piccard in the late 1930s. The principle was now also to be applied under water. When an empty tank was flooded with water, the deep sea submarine sank, not rising again until the water was pumped out of the tank. Unmanned, 'FNRS-2' reached depths up to 1,400 metres, but it was ultimately damaged by stormy seas.

In 1960, Jacques Piccard and Don Walsh reached the ocean floor of the Mariana Trench in the Bathyscaph 'Trieste'. During their 20-minute adventure, however, the submarine stirred up the sand so vigorously that the two men on board could not see much of their environment. In his article 'Man's Deepest Dive', Piccard vividly describes their adventurous dive.

In 1982, the Navy attempted to use industrial robots for underwater explorations. The goal was robots that not only moved, but that were also able to see their surroundings. They should be able to be reprogrammed offline and perform activities on ships. "Today's robots are far different from the versions dreamed up by science fiction illustrators. Today's working robots are often no more than sophisticated mechanical claws", says a report by the Navy of the time. Such claws had gripping arms with had a gripping arm with different adjustments.

1985: Robots discover the wreck of the <span class="st">RMS Titanic</span>

73 years after the sinking of the RMS Titanic, the deep sea robot 'Argo' set off to locate the wreck: a 'floating eyeball', about the size of a car. Robert D. Ballard was the researcher who conducted the underwater exploration. He found the Titanic at 3,800 metres below the ocean. It was an incredible experience for him, he said later. With the help of 'Argo', a complete profile of the Titanic could be created.

The unmanned research robot 'Kaiko' was the first ROV (Remotely Operated Vehicle) to reach the lowest point of the Mariana Trench: a place called Challenger Deep, 11,034 metres below sea level. This was a deep-diving record, which required a great deal of know-how regarding materials and technology because not every material survives pressure that is 1000 times stronger than the pressure of air on the Earth. 'Kaiko' was connected to its mother ship via a glass fibre cable and took samples from the seafloor. In addition to single cell organisms, it spotted a sea cucumber, a scale worm and a shrimp. In 2003, Kaiko's connecting cable to its launcher broke. Since then, it has been resting on the bottom of the Mariana Trench.

In 2001, the Max Planck Institute for Marine Microbiology investigated methane-eating bacteria, which deep sea robot 'Victor' had collected in the Norwegian Sea at a depth of 1,250 metres below the sea. The built-in camera enabled the researchers to control the robot from the ship. In addition to sulfur bacteria, the researchers discovered archaea on the underwater volcano Haakon Mosby: These are solitary animals from the early days of the Earth living in extreme habitats. According to marine biologist Antje Boetius, the archaea, together with these bacteria, can oxidize methane into carbon dioxide. They do not need any free oxygen to carry out this chemical conversion. A further development of the submersible robot is still in use today on the research vessel "Polarstern".

The first diving robot 'AUV Bluefin', was shaped like a small submarine and acquired by the Alfred Wegener Institute in 2003. "Autonomous underwater vehicles" (AUVs) are perfectly suited for long deployments on the ocean floor, as they can carry out marine research using wireless technology. The Bluefin's successor, 'AUV Abyss' can map the ocean floor using echoscopes and determine the physical parameters of the water column with various sensors. The device is powered by lithium batteries that allow it to dive up to 22 hours.

A new development at the Max Planck Institute for Marine Microbiology makes it possible to measure oxygen in the sediment of the seabed. The "crawler" also determines the speed of the metabolism which provides insights into the climate development of the Earth. A reaction of the oxygen with a dye in the tip of the probe produces fluorescence. This, in turn, is a measure of the amount of available oxygen.

The MARUM-QUEST deep sea robot collects samples in depths down to several thousand metres below sea level. Deep-sea hot springs spew hydrogen sulfide, ammonium, methane, iron, and hydrogen into the sea. "Organisms gain energy by oxidation of these substances; completely without sunlight," says Nicole Dubilier of the Max Planck Institute for Marine Microbiology in Bremen. This process of chemosynthesis, which is essential for life, allows the microorganisms to gain energy in the darkness of the deep sea.

In 2005, researchers from the University of Kiel and the Max Planck Institute for Marine Microbiology investigated a methane source on the seafloor before Costa Rica with the research diving vessel 'Alvin'. At a depth of 2,500 metres, they discovered a "forest" of tubeworms the size of two football fields. "We know these tubeworms from various smaller deposits in our working area and from other areas, for example, from central oceanic spines," said Kiel researcher Warner Brückmann from the Leibniz Institute for Marine Science. "However, we have not observed them so far in such a large number and density."The worms use the sulfide, which is released in the methane decomposition to survive in the deep sea. The tube-like shells in which they live protrude up to 1.5 meters from the sea floor.

The 'Benthic Rover' was the first robot to carry out measurements in the deep sea without interruption for six months. It was equipped with 96 alkaline D batteries and measured the oxygen consumption of organisms of the deep sea floor. With the help of its measurements, effects of sinking nutrients of the water surface on the deep sea became visible for the first time. The long-term studies made this robot indispensable for the researchers at the Monterey Bay Aquarium Research Institute. "The measured data show seasonal changes during a year," said Alana Sherman, the MBARI project engineer, in an interview with Wired magazine.

Submarine robot 'Wally' explores the seabed at the click of a mouse. The award-winning robot is controlled exclusively by Internet, transmitting video material and data from 900 metres below the water surface. The researchers at Jacobs University receive scientific and financial support from the Max Planck Institute for Marine Microbiology. From a distance of about 9,000 kilometers Wally sent live photos and videos of its 'meeting' with underwater creatures. "Research robot Wally combines highly developed deep sea- and sensor technology with the fundamentally simple idea that today's communication over the Internet nowadays transcends all temporal and spatial boundaries," said Martin Klinkhammer of the DFG Senate Commission on Future Directions in Geoscience.

The 'Crabster CR200' was designed for the most difficult undersea explorations: the researchers of the Korean Institute of Ocean Science and Technology, Bong Huan Jun, based the machine on the characteristics of crabs and lobster that live in stormy waters. This is why the six-legged underwater robot can also be used in strong currents, rough terrain, and deep waters. Its special feature is that it moves very slowly, crawling along the seabed at a speed of 10 centimeters per second. In the future, it will investigate marine wrecks in up to 200 metres of depth and identify and seal leaks in the case of oil spill incidents. Since it has no loud propeller, it does not disturb animals in their habitat.

Since July 2016, the mobile underwater 'Tramper' has been performing oxygen measurements of the soil in 2,500 meters of water on the seabed of the Arctic west of Spitzbergen. Dead plants and animals are degraded by microorganisms and deliver oxygen. The material cycle changes during a year. For a period of twelve months, researchers from the Alfred Wegener Institute and the Max Planck Institute for Marine Microbiology are collecting data on how the Arctic seabed responds to environmental changes.